Check Engine Request

If an emission-related fault arises in the automatic transmission, the transmission control module sends a PWM signal at a frequency of 2 Hz from pin 5 to engine control module pin:
^ 61 (Saab Trionic)
^ 65 (Motronic 4.1)
^ 39 (Motronic 5.2)

The engine control module then causes the CHECK ENGINE lamp (MIL) to light up.

When the ignition switch is turned to the ON position, the control module sends a ground pulse for 1 second as an operational check.